A-to-I editing as a mechanism for the reversion of G-to-A evolution. All mouse editing sites were converted to human genome coordinates. G-to-A ratio was calculated and fixed as 1 (left). All human editing sites were converted to mouse genome coordinates; G-to-A ratio was calculated and normalized (right), exhibiting 1.66-fold enrichment compared to the mouse-to-human conversion. (*P = 10-7, Fisher’s exact test).